Process of preparing lithographic plates



Al1g- 1967 J. A. CUZNER ETAL 3,335,072

PROCESS OF PREPARING LITHOGRAPHIC PLATES Filed June 1, 1964 INVENTORS JOSEPH A. CUZNER 1 ATTORNEY United States Patent 3,335,072 PROCESS OF PREPARING LITHOGRAPHIC PLATES Joseph A. Cuzner, Trotwood, and Krishnan R. V. Pandalai, Dayton, Ohio, assignors to Martin-Marietta Corporation, New York, N.Y., a corporation of Maryland Filed June 1, 1964, Ser. No. 371,304 8 Claims. (Cl. 20417) The present invention relates to planographic printing plates and more particularly, to a process for manufacturing printing plates.

It is known to provide a deep etch lithographic plate made essentially of aluminum (including alloys rich in aluminum) having an ink-receptive copperized portion on the surface thereof. In the past, copper has been chemically deposited upon the selective portions of a masked and generally grained aluminum surface by means of the replacement of copper ions in a solution by aluminum metal from the surface due to a typical oxidation-reduction reaction. The resultant chemical deposit generally has a large grain size and is very porous, due to the nature of the replacement reaction. Due to the large grain size and porosity of the copper deposit, lithographic plates made in this manner have limited useful press lives because of poor adhesion.

In view of the foregoing, the art has sought a method of producing more wear resistant coatings of copper on aluminum by reducing the grain size and porosity, thus obtaining better adhesion. Electrolytic deposition of copper has been suggested. However, electrolytes from which copper may be electrodeposited must not deleteriously affect the light-hardened masks ordinarily employed by photo-lithographers. As far as we are aware, there has not, prior to the present invention, existed a process for electrodepositing copper or like ink-receptive metals on an aluminum base which has been entirely commercially acceptable to workers in the lithographic field.

It has now been discovered that by means of a special electrolytic bath composition in conjunction with controlled electrodeposition conditions, copper can be deposited on aluminum in a manner which is industrially satisfactory to the lithographic art.

It is an object of the present invention to provide a novel process for the electrodeposition of copper on alu-- minum.

It is a further object of the present invention to provide a novel copper-electroplating bath.

An additional object of the present invention is to provide a novel process of preparing a lithographic plate.

Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the drawing in which:

FIG. 1 is a cross-sectional view of a masked lithographic plate blank prior to copperizing; and

FIG. 2 is a cross-sectional view of the plate-blank of FIG. 1 together with an anode assembly and electrolyte during electrodeposition.

Generally speaking, the present invention contemplates a process of electrodeposition of copper on aluminum which comprises passing a substantially unidirectional current at about room temperature between a copper anode and an aluminum cathode at a potential difference of about 3.5 to about 8 volts through a substantially waterfree electrolyte containing about 1 to about 30 grams per liter (g.p.l.) of copper as the chloride, bromide, iodide,

nitrate, sulfate or fluoborate. The substantially water-free electrolyte has as a liquid phase solvent, a mixture comprising advantageously about 7 parts by weight of a lowmolecular Weight polyalcohol, e.g., ethylene glycol and about 1 part by weight of a glycol ether which mixture is acidified with about 0.5% to about 2.0% by weight of a substantially anhydrous acid and/ or acid former selected from the group consisting of hydrogen chloride, hydrogen bromide, hydrogen iodide, nitric, sulfuric, and fiuoboric acids. Advantageously, the substantially water-free electrolyte also contains a small but effective amount of a nonionic surfactant or organic addition agent in order to assure satisfactory wetting of the surface to be plated.

As contemplated in accordance with the present invention, a low molecular weight polyalcohol includes glycols of'the aliphatic series, specifically, ethylene glycol, diethylene glycol, dipropylene glycol, propylene glycols, triethylene glycol and hexylene glycol. Glycol ethers include ethyl, methyl and n-butyl mono and di ethers of ethylene or diethylene glycol,

In ordinary photolithographic practice, a grained aluminum plate is coated with a light-sensitive coating such as the conventional gum arabic-dichromate coating. The coated plate is then exposed to light passing through a stencil or mask. The light-struck portions of the coating become hardened. A developer solution is them employed to remove the masked (unhardened) portions of the coating and the thus exposed portions of the plate are then etched. As an example, a solution containing lactic acid, calcium chloride and zinc chloride can be used as a developer. A solution containing the mixed chlorides acting as inhibitors for solution of the coating, together with ferric chloride and/ or hydrochloric acid can be used as the etchant. A plate, as it might appear in greatlyma-gnified cross-section, at this stage of the process is depicted in FIG. 1 of the drawing. Referring now thereto, it is to be noted that aluminum base 11 has superimposed thereon hardened coating 12 covering selccted areas of the surface 13. Exposed surface areas 14 are in the etched condition. After etching the plate is washed, advantageously with anhydrous alcohol and dried. The plate is then ready for electrodeposition. During electrodeposition, consisting essentially of electrolytic deposition of metal at the interface between the metal of the plate and the electrolyte, the plate appears substantially as depicted in FIG. 2. Referring now thereto, it is to be noted that copper anode 15, backed by insulating block 16, covered with soft textile pad 17 and connected to a current source by connect-or 18, ride on top of hardened coating 12 in a pool of nonaqueous electrolyte 19. By means of the passage of a substantially unidirectional electric current between anode 15 and cathode 11, copper deposit 20 forms on etched surface 14 of cathodic base 11. When an electrolyte in accordance with the present invention is employed under the conditions set forth herein, copper deposit 20 adheres firmly to surface 14 and forms a wear-resistant, ink-receptive surface that is highly advantageous when compared to copper deposits of the prior art. The synergistic interaction between the electrolyte of the present invention and the coatings of the prior art is depicted in FIG. 2 in that anode 15 and its associated elements can be passed across the surface of hardened coating 12 without disturbing the coating and thus long lasting, highly detailed, printing plates can be made by means of the process of the present invention.

After the ccpperizing process is complete, the plate is washed, advantageously with absolute alcohol, dried, lacquered with a lacquer such as a vinyl lacquer and developing ink is applied thereto. Only then is the original hardened coating 12 removed from the plate by washing with water. Under particular circumstances, certain conventional lithographic process operations may be eliminated. Thus, etching of the plate prior to electrodepositing can be minimized and, lacquering after plating may be eliminated.

In carrying out the present invention, it is highly advantageous to employ an electrolyte as set forth in the following table.

The electrolyte of the foregoing table is advantageously employed at about room temperature, e.g., about 60 F. to about 80 F. with a potential difference of about 4 volts (meter reading) between a padded copper anode and the aluminum cathode. The required voltage can be supplied by batteries but, advantageously, a transformer-rectifier unit is employed to change normally supplied 115 volt 6O cycle A.C. line current to the required D.C. voltages. Other ingredients such as sulfonic acids, amines, organic acids and other conventional organic addition agents can be used in the electrolyte for various purposes. Likewise, plate coatings other than dichromate-gum arabic can be used. For example, coatings having a base of natural or synthetic gums, cellulose and starch derivatives or polymers and sensitized with materials such as azides, diazos or dichromates can also be employed. The coatings may also include substances such as iodide ion, thiocyanate ion or the like to further inhibit deposition of copper on the coated areas. Further, specialized electroplating process techniques such as periodic reversal of current, non-uniform current flow and the like may be usefully employed under specialized circumstances.

Electrodepositable metals, having ink-receptive properties, and having alcohol and/ or glycol soluble salts, e.g., nickel or zinc, may be present in the electrolyte to replace part or all of the copper.

For the purpose of giving those skilled in the art a better understanding and/ or appreciation of the advantages of the present invention, the following specific example is given in comparison to prior art practice.

Example An aluminum plate pretreated to be in the condition as illustrated in FIG. 1 is coated with copper in accordance with the present invention with a potential difference of 4 volts and with a pool of electrolyte having the composition tabulated as follows until a satisfactory deposit is obtained.

Aqueous hydrochloric acid is employed. It is to be understood that the Water contained in such aqueous acidic solutions is incorporated into the plating bath in amounts up to about 4 parts by weight, in 100, and for the purpose :of the invention such baths are considered substantially anhydrous.

Udylite UBAC Isopropyl is a designation of a proprie- -tary electroplating additive in isopropyl alcohol solution the use of which is advantageous but not essential to the operation of the present invention.

The time of plating will depend upon the size and type of aluminum plate and the atmospheric conditions at the time of plating. Normally, between two and five minutes is sufficient plating time. The plate is then washed, dried, lacquered, coated with developing ink and the light hardened coating removed.

A similarly pretreated plate is coated wtih copper by chemical replacement from a solution containing and is then finished in like manner to the electrodeposited plate. Under ordinary commercial printing conditions the electrodeposited copper plate has given twice or more as many satisfactory impressions as the plate having the chemical replacement deposit.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, such as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

Having thus described our invention, we claim:

1. A process particularly applicable in the production of lithographic plates for depositing ink-receptive metal on aluminum which comprises electrochemically depositing said metal on said aluminum at a liquid-solid interface between a cathodic aluminum base and a solution of an alcohol-soluble salt of said metal in an essentially waterfree acidified mixture of a low-molecular weight liquid polyalcohol and a glycol ether.

2. A process particularly applicable in the production of lithographic plates for depositing copper on aluminum which comprises electrochemically depositing said copper on said aluminum at a liquid-solid interface between a cathodic aluminum base and a solution of an alcohol-soluble salt of said copper in an acidified mixture of a lowmolecular weight liquid polyalcohol and a glycol ether.

3. A process of producing a lithographic plate comprising in sequence exposing at least a part of an aluminum plate having a light sensitive coating thereon to actinic radiation to harden the so-exposed portion of said coating, washing away that portion of the coating which was not so exposed, electrochemically depositing a layer of copper on said etched surfaces from a bath containing an alcoholsoluble salt of copper dissolved in a substantially water free acidified mixture of a low molecular weight liquid polyalcohol and a glycol ether, developing the electrodeposit with a developing ink and thereafter removing the remaining portions of said light-sensitive coating.

4. A process as in claim 3 wherein the copper salt is copper chloride and the electrodeposition is carried out at a potential difference of about 2 to 8 volts.

5. A process as in claim 3 wherein the polyalcohol is ethylene glycol, the glycol ether is diethylene glycol nbutyl ether and the ratio between the polyalcohol and the glycol ether is about 7 to l.

6. An electrolyte for electrochemical deposition comprising about 1 to about 30 grams per liter of metal selected from the group consisting of copper, zinc and nickel as a salt selected from the group consisting of the chloride, the bromide, the iodide, the sulfate, nitrate and the fluoborate dissolved in a substantially anhydrous, acidified mixture selected from the group consisting of ethylene, diethylene, dipropylene, propylene, triethylene and hexylene glycol and a glycol ether selected from the group consisting of the ethyl, methyl and n-butyl ethers of ethylene glycol and diethylene glycol.

7. An electrolyte for electrochemical deposition com- 5 6 prising about 1 to about 30 grams per liter of copper as a References Cited salt selected from the group consisting of the chloride, the UNITED STATES PATENTS bromide, the iodide, the sulfate, the nitrate and the fluoborate dissolved in a substantially anhydrous, acidified 902,755 11/1908 Meyer i 204-14 mixture of a low molecular weight glycol and a glycol 5 2,708,655 5/1955 Turner 204 33 ether.

8. An electrolyte as .in claim 7 wherein the salt is the JOHN MACK Prlmary Examiner chloride. T. TUFARIELLO, Assistant Examiner. 

1. A PROCESS PARTICULARLY APPLICABLE IN THE PRODUCTION OF LITHOGRAPHIC PLATES FOR DEPOSITING INK-RECEPTIVE METAL ON ALUMINUM WHICH COMPRISES ELECTROCHEMICALLY DEPOSITING SAID METAL ON SAID ALUMINUM AT A LIQUID-SOLID INTERFACE BETWEEN A CATHODIC ALUMINUM BASE AND A SOLUTION OF AN ALCOHOL-SOLUBLE SALT OF SAID METAL IN AN ESSENTIALLY WATERFREE ACIDIFIED MIXTURE OF A LOW-MOLECULAR WEIGHT LIQUID POLYALCOHOL AND A GLYCOL ETHER. 